Ratio: finding a missing amount

The Maths Habit

Jo makes squash. Each box is one cup. She makes a bigger jug. Which jug tastes the same as Jo’s?

Jo’s jugSquashWater
ASquashWaterToo strong
BSquashWater✓ The same: every bar doubled
CSquashWaterFar too strong

The number at the end is what the whole bar is worth. How much is one box?

126
124
205

Ratio
It tells you how many parts of each thing there are.
2 : 3CatsDogs
Part
One box of a bar. Every part is the same size.
Cats✓✓Dogs✓✓✓
Amount
How much there is of one thing.
Cats1010 cats

CatsamountDogs?
amount÷its parts=one part
  1. 1Draw the bars.One bar for each thing. One box for each part. Write the amount you know at the end of its bar.
  2. 2Find one part.Divide the amount you know by its parts.

Cats and dogs are in the ratio 2 : 3. There are 10 cats. How much is one part?

1Draw the bars.
Cats5510Dogs555?
2Find one part.
10÷2=5

Pens and rulers are in the ratio 3 : 1. There are 12 pens. How much is one part?

1Draw the bars.
Pens44412Rulers4?
2Find one part.
12÷3=4

Cats and dogs are in the ratio 2 : 3. There are 10 cats. How much is one part?

1Draw the bars.
Cats5510Dogs555?
2Find one part.
10÷2=5
12amount÷its parts=one part

Cups and plates are in the ratio 4 : 3. There are 20 cups. How much is one part?

1Draw the bars.
Cups555520Plates555?
2Find one part.
20÷4=5

Cats and dogs are in the ratio 2 : 3. There are 10 cats. How much is one part?

1Draw the bars.
Cats5510Dogs555?
2Find one part.
10÷2=5
12amount÷its parts=one part

Boys and girls are in the ratio 2 : 5. There are 15 girls. How much is one part?

1Draw the bars.
Boys33?Girls3333315
2Find one part.
15÷5=3

Cats and dogs are in the ratio 2 : 3. There are 10 cats. How much is one part?

1Draw the bars.
Cats5510Dogs555?
2Find one part.
10÷2=5
12amount÷its parts=one part

Vans and cars are in the ratio 1 : 4. There are 8 cars. How much is one part?

1Draw the bars.
Vans2?Cars22228
2Find one part.
8÷4=2

12amount÷its parts=one part

1Apples and pears are in the ratio 1 : 2. There are 5 apples. How much is one part?

1Draw the bars.
Apples55Pears55?
2Find one part.
5÷1=5

2Bikes and cars are in the ratio 3 : 1. There are 9 cars. How much is one part?

1Draw the bars.
Bikes999?Cars99
2Find one part.
9÷1=9

3Cats and dogs are in the ratio 2 : 5. There are 20 dogs. How much is one part?

1Draw the bars.
Cats44?Dogs4444420
2Find one part.
20÷5=4

4Pens and rulers are in the ratio 5 : 3. There are 35 pens. How much is one part?

1Draw the bars.
Pens7777735Rulers777?
2Find one part.
35÷5=7

One part is 5. How much is each bar worth?

5510
55515
555520

CatsamountDogs?
amount÷its parts=one part
one part×other parts=missing
  1. 1Draw the bars.One bar for each thing. One box for each part. Write the amount you know at the end of its bar.
  2. 2Find one part.Divide the amount you know by its parts.
  3. 3Find the missing amount.Multiply one part by the other bar’s parts.

Cats and dogs are in the ratio 3 : 4. There are 12 cats. How many dogs are there?

1Draw the bars.
Cats44412Dogs4444?16
2Find one part.
12÷3=4
3Find the missing amount.
4×4=16

Pens and rulers are in the ratio 2 : 5. There are 8 pens. How many rulers are there?

1Draw the bars.
Pens448Rulers44444?20
2Find one part.
8÷2=4
3Find the missing amount.
4×5=20

Cats and dogs are in the ratio 3 : 4. There are 12 cats. How many dogs are there?

1Draw the bars.
Cats44412Dogs4444?16
2Find one part.
12÷3=4
3Find the missing amount.
4×4=16
12amount÷its parts=one part3one part×other parts=missing

Cups and plates are in the ratio 3 : 2. There are 15 cups. How many plates are there?

1Draw the bars.
Cups55515Plates55?10
2Find one part.
15÷3=5
3Find the missing amount.
5×2=10

Cats and dogs are in the ratio 3 : 4. There are 12 cats. How many dogs are there?

1Draw the bars.
Cats44412Dogs4444?16
2Find one part.
12÷3=4
3Find the missing amount.
4×4=16
12amount÷its parts=one part3one part×other parts=missing

Boys and girls are in the ratio 3 : 5. There are 25 girls. How many boys are there?

1Draw the bars.
Boys555?15Girls5555525
2Find one part.
25÷5=5
3Find the missing amount.
5×3=15

Cats and dogs are in the ratio 3 : 4. There are 12 cats. How many dogs are there?

1Draw the bars.
Cats44412Dogs4444?16
2Find one part.
12÷3=4
3Find the missing amount.
4×4=16
12amount÷its parts=one part3one part×other parts=missing

Vans and cars are in the ratio 2 : 7. There are 6 vans. How many cars are there?

1Draw the bars.
Vans336Cars3333333?21
2Find one part.
6÷2=3
3Find the missing amount.
3×7=21

Ratio: finding a missing amount worksheet, page 1

Ratio: finding a missing amount worksheet, page 2

Answer sheet

Is it right?
Thumbs up: right. Thumbs down: wrong.

  1. Red : blue is 1 : 3. There are 5 red, so 15 blue.

    Right

  2. Red : blue is 2 : 5. There are 10 red, so 13 blue.

    Wrong: added on

  3. Red : blue is 3 : 4. There are 12 red, so 9 blue.

    Wrong: wrong bar

  4. Red : blue is 2 : 3. There are 8 red, so 12 blue.

    Right

  5. Red : blue is 4 : 5. There are 20 red, so 21 blue.

    Wrong: added on

  1. Squash and water are mixed in the ratio 1 : 4. Jo uses 50 ml of squash. How much drink does she make altogether?

    250 ml

  2. Red, white and blue flowers are in the ratio 2 : 3 : 5. There are 18 white flowers. How many red flowers are there?

    12

  3. These two ratios are equal. Find the missing number.  ? : 12 = 5 : 4

    15

  1. Cats and dogs are in the ratio 2 : 3. There are 8 cats. How many dogs?

    12
    1Draw thebars.Cats8Dogs?2Find one part.÷=3Find the missingamount.×=

  2. Boys and girls are in the ratio 3 : 5. There are 25 girls. How many boys?

    15
    1Draw thebars.Boys?Girls252Find one part.÷=3Find the missingamount.×=

  3. Pens and rulers are in the ratio 4 : 7. There are 16 pens. How many rulers?

    28
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